avconv: Encoder 'aac' is experimental and might produce bad results. Add '-strict experimental' if you want to use it.

I was trying to rotate some of videos from my iPhone on ubuntu using avconv (ffmpeg).
After a quick googling, I got this command (http://askubuntu.com/a/228588):

avconv -i in.mov -vf "transpose=1" out.mov

In case of my videos, it failed with: 

Encoder 'aac' is experimental and might produce bad results. 
Add '-strict experimental' if you want to use it.

To save you some time, here is how to put the parameter correctly:

avconv -i in.mov -vf "transpose=1" -strict experimental out.mov

Note: I wasn't investigating the cause of it, or any better solutions, because this just worked for me. 

Enjoy!